1. Field of the Invention
This invention relates to tape guiding in a magnetic tape transport, and in particular to improved guiding providing precise control of tape position relative to the tracks of a magnetic transducer.
The invention, as well as the prior art, will be described with reference to the figures of which:
FIG. 1 is a perspective view of the elements comprising the tape path of a magnetic recorder known in the prior art,
FIG. 2 is a plan view of the elements comprising the tape path illustrated in FIG. 1,
FIG. 3 is a perspective view of elements comprising the tape path of a magnetic recorder according to the teaching of the invention, and
FIG. 4 is a side elevation view of the elements of the tape path illustrated in FIG. 3.
2. Description Relative to the Prior Art
The guiding of the tape over a magnetic transducer of a magnetic tape transport is a critical design consideration in magnetic recorder design. In the prior art, many guide designs have been employed including fixed and rotating guides, cylindrical and crowned guides, and flanged and unflanged guides. Typically, the tape is unspooled from a supply reel, engages one or more guides for locating the tape relative to some reference plane, traverses a magnetic transducer located with respect to the reference plane whereby the tape is positioned with respect to the record/reproduce tracks of the transducer, leaves the transducer, re-engages one or more additional guides, and then spools onto a takeup reel. One purpose served by a guide is to change direction of the tape motion, and another important use is the precise positioning of the tape as it approaches, traverses and leaves the transducer. This positioning requirement is of utmost importance for tape tracking with multitrack magnetic heads, and the requirement becomes more stringent as the number of tracks increase and, attendantly, each track width dimension decreases.
Referring to FIG. 1, a typical configuration of a magnetic transducer and guides of the prior art illustrates a tape 10 in contact with fixed flanged guides 12, 18 and a multitrack transducer 14. The transducer 14 may be an erase head, a record head, a reproduce head, or a record/reproduce head. The cut away section of the tape 10 reveals the line of gaps 15 and tracks e.g. 17, 19 of the transducer 14. The tape 10, guided by the guide 12, and under tension T, approaches the transducer 14, and after leaving the transducer 14 engages the second guide 18. The guides 12, 18 are elements whose 21, 23 bases are accurately planar and whose axes are perpendicular to the bases. The distances between the upper and lower flanges of the guides 12, 18 are held to a dimension just over the maximum specified width of the tape 10. Similarly, the base of the transducer 14 is planar and the cylindrical tape contacting surface of the transducer 14 and its line of gaps 15, are perpendicular to the transducer base. (The phrase "line of gaps" is used generically, and includes the single track transducer case where it is equivalent to the phrase "gap line".) The guides 12, 18 and the transducer 14 are mounted on a plate 20 whose top surface 22 serves as a reference plane. The tape 10 is guided by being positioned between the upper and the lower flanges of the guides 12, 18. Because the guides 12, 18 and the transducers 14 are referenced to the same surface 22, the tape is resultantly positioned with respect to the tracks e.g. 17, 19 of the transducer 14. It will be noted that the prior art teaches that the axes of the guides 12, 18, and the line of gaps 15 of the transducer 14 are mutually parallel and perpendicular to the reference plane 22, and the plane of the magnetic tape 10 is attendantly perpendicular to the reference plane 22.
Referring to FIG. 2 which is a plan view of the tape, guide and transducer configuration of FIG. 1 the tape 10 is shown in contact with the cylindrical surface of the transducer 14 over an angle .theta., defined as the "tape wrap angle", and for a transducer having a radius R, the length of the arc of tape-head contact is equal to R.times..theta. when .theta. is expressed in radians. It will be seen that with the tape under a tension T, a force F normal to the transducer surface is applied by the tape to the transducer.
When guided as described above, the tape 10 may laterally wander in the direction of the axes of the guides within the constraints established by the upper and lower flange positions with resultant misregistration of the tape and the transducer tracks. Spring loading of one flange to urge the tape against a fixed second flange has been practiced with the goal of eliminating this lateral motion, but the resultant guides are mechanically complex and prone to edge damage the tape. Other guide geometries of varying complexity have also been advanced as solutions to the problem.
The present invention provides guiding of simplicity, reliability and precision which provides accurate registration of the tape and transducer tracks.